The present invention relates to the monitoring of galvanometer bearing performance; and more particularly to analyzing the response to position commands for information about bearing condition.
One of the fundamental operating components of galvanometer systems are bearings. Bearings and the peripheral components allow the high speed and precision operation of scanners and similar devices.
However, bearings are subject to stress and damage from the physical contact and environmental conditions. As the bearings begin to wear or develop divets, the tolerance of the entire system degrades. Other causes for degradation includes the bearing interface with the race assembly. Due to the degrading performance, eventually the system falls out of tolerance and requires maintenance. In some situations, bearing failure can shut down a critical manufacturing line or other high priority operation. Parts and personnel may not be at beckon call to repair the system.
In addition, due to the precise manufacturing requirements, the bearings may suffer from design problems or manufacturing defects that do not comply with the system requirements. Such errors require a means to detect and quantify the error in order to notify the manufacturer and maintain the high quality of the product.
There have been some attempts to alleviate the aforementioned problems. In U.S. Pat. No. 4,326,677, a monitoring circuit for detecting metallic contact between the high-speed spindle and the housing is disclosed. Such a condition alerts personnel to this condition to avoid more serious problems.
Another monitoring circuit is shown in U.S. Pat. No. 5,226,736, wherein sensors measure the dimensions of cracks or pits in the race or between the race and rings. The data is communicated to the processing center that analyzes the data for fault conditions.
What is needed is a means of detecting bearing tolerance changes over time. Such a system would be able to detect variations in the operating performance of a galvanometer bearing set and alert operators to potential problems. Such a monitoring and detection system must be simple and cost-effective to use and operate, and be passively transparent such that it does not interfere with normal operation of the galvanometer device or system. One of the advantages of such a system would be to incorporate a tolerance margin that could be used by maintenance personnel to anticipate failures in advance, so that the necessary replacement or repair parts would be in stock and the unit scheduled for downtime and service prior to an actual failure.
Accordingly, an object of the present invention is to provide a methodology for the qualifying and monitoring of the bearings of rotary servo systems, such as galvanometer scanners, for bearing performance and condition. A position error signal is measured and recorded as compared to the command angle. Certain anomalies that may be outside the normal threshold limits of amplitude are isolated and analyzed. The position error signal is a difference signal and can therefore be magnified to provide highly accurate measurements.
Another object is to isolate the bearing damage from electrical contamination or other signal conditions that are not angular position dependent. A DC offset ramp is applied to the position error signal and analyzed for anomalies in the error signal that move coherently with the position error signal, indicating positional dependence and a likelihood of bearing damage.
A further object is to gather additional information from the signal processing. The amplitude of the anomaly is a measure of the degree of bearing damage. The width or duration of the anomaly as compared to command signal range is a measure of the angular range of the damaged region. The angular position of the damaged region is measured by the offset voltage at which it appears, as compared to the range over which the device is operated.
A further object of the invention is to incorporate pre-determined tolerance limits such that as the bearing damage reaches a specific degree of damage, an alarm would alert the user for scheduling repair/replacement and procurement of the required parts and equipment before a catastrophic, unscheduled failure occurs.
Another object is to qualify the bearings of individual servo devices or types of devices, by measuring the characteristics and storing the information for later tracking and comparison. Such information provides a means of tracking performance of a particular set of bearings and also as a means of approving or accepting a lot of bearings from a manufacturer. In essence, it provides a standard for acceptability and a baseline for operational evaluation.
And yet a further object is to qualify other elements of the device such as lubricants, ball sphericity, race finish, and similar parameters affecting the functioning of the bearings. Such parameters would be analyzed and the information used for assessing the improvement or degradation of performance provided by design or configuration changes.
The position error signal of a servo system is commonly measured as part of a setup or diagnostic routine. Such diagnostics can be used not only to verify system performance as part of final random inspection, but also to qualify components such as bearings or lubricants. The position error signal enables the manufacturer to quantify the acceptance level and establish a means for checking component consistency.
The position error signal is not generally measured by the operational controller elements of rotary servo systems such as those of scanners. However the present invention indicates the importance of the position error signal for real time monitoring of bearing condition, and it is a requirement of the invention to have the position error signal enabled in some manner such as within the scan controller of a galvanometer scanner.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only a preferred embodiment of the invention is described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.